This invention relates to klystrons and, more particularly, to the tuning of klystron oscillators.
Multiple cavity klystron oscillators are employed for the generation of carrier signals at microwave frequencies, for example, at X band. In order to select a specific frequency of oscillation, it has often been the practice to provide a diaphragm in a wall of each of the cavities, the diaphragm being deformable so that the frequency may be raised by pressing the diaphragm inwardly to decrease the volume of a cavity, the frequency being lowered by pulling the diaphragm outwardly to increase the volume of the cavity. The cavity walls are typically made of copper of sufficient thickness to maintain dimensional stability while the diaphragms are made substantially thinner than the walls and brazed thereto for a vacuum tight seal.
A problem arises in that in the commercial production of klystron oscillators, the central frequency of the tuning band is desirably set at different values for different applications of the klystron. To accomplish the selection of the center frequency of the tuning band, it has been the practice to prestress the tuning diaphragm, as by a tuning screw attached to the klystron outside the cavity. Thereupon, the diaphragm may be further deformed to accomplish the desired tuning within the tuning range. However, it is noted that the diaphragm is thereby utilized both for establishing a bias frequency as well as for the range of frequencies about the center of the tuning band. As a result, the combination of deformation employed for the initial adjustment as well as for the subsequent tuning has produced premature fatigue in the material of which the diaphragm is fabricated. Accordingly, the total number of tuning operations for selecting a desired frequency is significantly limited.